German Patent 21 14 160 discloses a sintered material that is made of an iron-based material to which carbon and lead as well as other alloy ingredients are added. This sintered material is said to have increased thermal conductivity compared with previously known materials. Thermal resistance and erosion resistance of the valve seat rings made from the sintered material are also said to be increased. However, relatively low limits are placed on the increase in thermal conductivity and in erosion strength, because the matrix material is an iron-based material.
A valve seat ring for a reciprocating piston internal combustion engine is disclosed in German Patent Disclosure Document DE-OS 35 28 526. There the valve seat is formed of two rings, of which the inner valve ring, disposed on the seat face of the valve, comprises a heat-resistant material of great hardness not made by powder metallurgy, while the outer ring in the seat comprises a material that has good thermal conductivity and is likewise not made by powder metallurgy. However, it should be noted that the greatest heat arises in the vicinity of the seat face of the valve and hence of the inner valve ring. From there it is supposed to be dissipated first through the inner valve ring and then through the outer seat ring. The thermally resistant material provided for the inner valve ring, having great hardness, is only slightly suited for this purpose, because it has merely conventional thermal conductivity.